I've been doing a lot of reading here about lift pump failures. What I'm wondering is, does anyone know the cause of the failure? I took one apart today and was wondering if you turned the impeller vanes around, if it would make the pump work again? Or has this already been tried.

 

There are check valves in the pump and over time the seat in the valve gets hammered after being slammed closed thousands of times causing fuel to leak past. Hence very little pumping effort. On mine the pump would quickly hit 15psi then, the pressure relief (15 PSI) would open, but it wouldn't close to hold 15psi, making pressure drop down to about 2 without the truck running. Just my personal experience.

 

I started a thread a few months ago looking for old LP's to BUY so I could tear them apart and see if I could find a common cause of the failures, but I got no response.

I think the check valves are suspect as in the previous post, but I also think a major cause of early failure is vibration. When you took it apart did you take the canister off? These are delicate pumps, I mean they are tough enough, but in the bottom of the canister is a circuit board. Mine had a resitor (or something similar) broken. It looks like its completed a circuit to a heater or something. Vibration is VERY tough on electical components, and this pump is bolted right to the block of a vibrating beast!

JUST MY $.02

 

No I just took the 3 bolts on the top out.

 

Take a grinder and grind off the bowl where the two are put togeather. There is a rubber gasket between the top unit and the bowl. Its pretty cool inside. The whole motor is flooded with diesel for cooling and lube. It will make you thing twice about dumping just anything in your tank and hope your filter gets it. This pump is PRE filter too!

Some guys dumped used oil in their fuel. All of the contaimination in the oil floods the motor, contacts, and rotor. Take one apart and you will never do that again! The perment motor magnets are flooded with fuel also. Any metal particles attach them selves to the magnets.

 

A lot of the problems with the pumps are caused by cavitation due to air being present in the fuel.....A FASS or Air Dog removes much of the air.

 

Yes but fass and airdog replace lift pump

 

Isn't the pressure supposed to drop to about 2 prior to starting so it is easier to start the engine?

 

Actually, I think its suppose to pump up then drop to zero before start up. Thats what mine does anyway and I just replaced it.

 

So does the FASS as it plugs into the factory harness.